1. Field of Invention
The present invention relates to a shielded reflective light-emitting diode (hereinafter also referred to as “shielded reflective LED”) having a light source including a light-emitting element, a reflecting mirror provided opposite to the light source, and a light-shielding member. Incidentally, in this specification, an LED chip itself is called a “light-emitting element”, a light-emitting substance including an optical device such as a package resin or a lens system in which an LED chip is mounted is called a “light source”, and a light-emitting device having a light source mounted therein is called a “light-emitting diode” or an “LED” as a whole.
2. Description of the Related Art
As a light-emitting diode used in a full color display, there is known a light-emitting diode having three light-emitting elements which emit light in three primary colors R, G and B respectively and which are mounted on one lead frame and sealed with a resin. An example of this related-art polychromatic LED will be described with reference to FIGS. 10A and 10B. FIGS. 10A and 10B are a plan view and a longitudinal sectional view showing the overall configuration of the related-art polychromatic LED.
As shown in FIGS. 10A and 10B, in the polychromatic LED 21, a red light-emitting element 22R, a green light-emitting element 22G and a blue light-emitting element 22B are mounted on a bottom surface of a concave reflecting mirror 23c which is formed on one lead 23a. Other three leads 23R, 23G and 23B extended to the vicinity of the lead 23a are bonded and electrically connected to the red light-emitting element 22R, the green light-emitting element 22G and the blue light-emitting element 22B by three wires 24R, 24G and 24B respectively. The three light-emitting elements 22R, 22G and 22B, the concave reflecting mirror 23c, the three wires 24R, 24G and 24B and part of the leads 23a, 23R, 23G and 23B are sealed with a transparent epoxy resin 25. At the same time, an ellipsoidal convex lens 26 is molded of the transparent epoxy resin 25. The major-diameter-direction length of the polychromatic LED 21 is 7.5 mm. A plurality of this type polychromatic LEDs 21 are arranged at intervals of 10 mm pitch on a substrate to thereby form a full color display.
When such polychromatic LEDs 21 are to be mounted on a surface, however, the influence of heat distortion based on the difference in thermal expansion coefficient between the sealing resin and the metal of the lead portions at a high temperature near 200° C. for surface mounting becomes larger because the length of each polychromatic LED 21 in the direction of the major diameter thereof is large to be 7.5 mm. As a result, the probability that the wires 24R, 24G and 24B will be broken increases, so that the percentage of defective products increases. Moreover, the respective light-emitting elements 22R, 22G and 22B vary in luminous intensity and chromaticity. For example, some green light-emitting elements 22G emit bluish green light or yellowish green light. The yield is lowered as well as much labor is required for selecting light-emitting elements in advance and mounting the selected light-emitting elements, because classification by luminous intensity and classification by chromaticity must be combined with each other. Hence, it is impossible to combine well-matched light-emitting elements 22R, 22G and 22B in order to eliminate such variations in luminous intensity and chromaticity. As a result, display unevenness in color and brightness arises in the full color display. Moreover, because the respective light-emitting elements 22R, 22G and 22B vary in characteristic of luminous intensity distribution, color balance of each color varies in accordance with the viewing direction so that the resulting color may be recognized as a different color. In addition, because three kinds of light-emitting elements emitting light in three colors respectively are provided for one condenser lens, there is a problem that axial displacement occurs in light radiated from the polychromatic LED 21.
Next, a light-emitting diode (hereinafter abbreviated also to “LED”) called “reflective LED” is a kind of device. Referring to FIG. 9, an example of the reflective LED will be described. FIG. 9 is a sectional view showing an example of the reflective LED. As shown in FIG. 9, the reflective LED 31 is configured so that a light-emitting element 32 is mounted on a forward end of one 33b of a pair of leads 33a and 33b through which electric power is supplied to the light-emitting element 32. The light-emitting element 32 and the other lead 33a are bonded and electrically connected to each other by a wire 34. The light-emitting element 32, the pair of leads 33a and 33b and the wire 34 are sealed with a transparent epoxy resin 35. At the same time, the transparent epoxy resin 35 forms a reflecting surface shaped like a paraboloid of revolution with the light-emitting element 32 as its focal point so that the reflecting surface is disposed opposite to the light-emitting element 32. Aluminum vapor deposition is applied onto an outside of the reflecting surface so that a concave reflecting mirror 36 is formed on the outside of the reflecting surface.
When light is emitted from the light-emitting element 32, the light is reflected by respective portions of the reflecting mirror 36. The reflected light advances upward in parallel with the center axis of the reflecting surface shaped like a paraboloid of revolution. Then, the light is radiated to the outside from a flat light-radiating surface 37 which is an upper surface of the reflective LED 31. In this manner, the reflective LED 31 is configured so that light emitted from the light-emitting element 32 can be radiated out as light condensed with high efficiency.
The area of the reflecting surface of the reflective LED 31 viewed from the outside is, however, so large that dark noise (pseudo-lighting) due to reflection of external light occurs largely when the reflective LED 31 is turned off. As a result, there arises a problem that contrast between light when the reflective LED 31 is turned on and light when the reflective LED 31 is turned off is low.